Manufacturing method of transfer unit

ABSTRACT

A diameter of middle section of at leas one of rollers, which are spanned by an intermediated transfer substance, is increased in respect to the diameter of end sections thereof by an amount which is determined in accordance with a degree of sub-scanning curvature of an image transferred onto a sheet.

This application, is based on Japanese Patent Application No. 2006-326903 filed on Dec. 4, 2006, in Japanese Patent Office, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a manufacturing method of a transfer unit used in an image forming apparatus such as an electro-photographic copying machine, a facsimile machine and a printer.

There are known various color image forming methods for the image forming apparatus. A method called tandem method is one of them. An image forming apparatus employing this tandem method is provided with, a photoconductive substance, light scanning device to write image data on the photoconductive substance, a plurality of image forming sections having a developing device to develop an electrostatic latent image formed on the photoconductive substance and a transfer units to transfer a toner image formed by each image forming section on the photoconductive substance onto a sheet.

As the image forming apparatus provided with the transfer unit, there is known an apparatus in which the toner image formed on the photoconductive substance is transferred onto an intermediate transfer substance (hereinafter call a transfer belt as well) in a shape of an endless belt of the transfer unit, then the toner image on the intermediate transfer substance is transferred onto the sheet. Since the image forming apparatus employing the intermediate transfer substance is able to superimpose the toner images formed on the photoconductive substance on the intermediate substance, it is popularly used in color image forming apparatus, which forms a color image on the sheet. In the color image forming apparatus, the color images of three colors i.e. yellow (Y), magenta (M) and cyan (C), or four colors where black (Bk) is added, are transferred and superimposed on the intermediated transfer substance, thereafter this superimposed toner image is transferred onto the sheet in a lump using an electrostatic force.

The toner images for respective colors formed on the photoconductive substance are transferred onto the intermediated transfer substance with predetermined timings so that color shifts do not occur when each color image is superimposed.

However, a plurality of rollers are spanned with the intermediate transfer substance with a certain tension, a distorted occurs in the rollers in a direction of a roller axis.

FIG. 1 shows an example of the image forming apparatus, FIG. 2 is a partial view of a transfer unit 60 in FIG. 1. FIG. 3 is a view showing a frame format of rollers 61 and 62 as seem from an arrow X1 in FIG. 2, which indicates a state where the rollers 61 and 62 spanned by the intermediate transfer substance 6 are distorted as mentioned above. Meanwhile, FIG. 3 shows that the rollers 61 and 62 in FIG. 3 are both straight rollers having the same diameter throughout entire width.

As FIG. 2 shows, if the rollers 51 and 62 distort in the axis direction, there is occurred a difference of a circumferential length between both ends sections and a middle section. Thus moving distances of the toner image transferred from the photoconductive substance to the intermediated transfer substance 6, until the toner image is transferred onto the sheet P differ between the both end sections and the middle section of the intermediated transfer substance 6, therefore a sub-scanning curve occurs in a sub-scanning direction (sheet conveyance direction) when the toner image transferred onto the intermediate transfer substance 6 is transferred onto the sheet P.

FIG. 4( a) is a diagram showing states of sub-scanning curves by respective colors, using line images as examples of the images of respective colors to be transferred, onto the sheet P, in case the photoconductive substances 1Y, 1M, 1C and 1K, and the intermediate transfer substance 8 are arranged as FIG. 1 shows. Here the sheet P is conveyed in an arrow W direction. The toner image, transferred onto the intermediated transfer substance 6 via the photoconductive substance 1Y is transferred onto the sheep P as a yellow toner image YL in FIG. 4( a). In the same manner, a cyan toner image CL, a magenta toner image ML and a black toner image Bk are transferred. As above understanding, the toner image transferred onto the intermediate transfer substance has more tendency to be effected in a portion near the rollers 61 and 62 and the sub-scanning curve is tend to occur.

As above, there was a problem that a high quality image can not be obtained due to color shift if the images of respective colors are transferred onto the sheet P in a state where the sub-scanning curve occurs for each color. FIG. 4( b) shows a state where the ends images are superimposed. Here a toner image CL for cyan color and toner image ML for magenta color are omitted. As the figure show, even if the end sections are matched in this manner, there is occurred color shift at the middle section.

Contrarily, there is disclosed a method that the curving of a scan line, a position of the scan line or inclination of the scan line are corrected by controlling a posture of an imaging element based on information from a color shift sensor arranged near the intermediated transfer substance through an actuator (for example Patent Document 1).

Patent Document 1: Tokkai 2004-286981

As above, the image forming apparatus using the intermediated transfer substance is popularly used as the color image forming apparatus which forms the color image of the sheet, since the toner images formed on the photoconductive substance can be superimposed on the intermediate transfer substance. However, since the sub-scanning curve occurs in the image, there was a problem that a high quality image can not be obtained due to the color shift at the time of color imposing. The method in the Patent Document 1 is to correct the sub-scanning curve of the image by correcting a writing beam to write the image data by controlling the pasture of the imaging element equipped in a light scanning device in the sub-scanning direction based on detected color shift.

Therefore, a device to control posture of the imaging element, device to correct the sub-scanning curve and the sensor to detect the sub-scanning curve were necessary, therefore the apparatus became complicated which increases the cost.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a transfer unit, which can inhibit the sub-scanning curve with a simple structure, capable of forming the high quality image without having color shift.

The above object can be achieved by the following. A manufacturing method of a transfer unit to transfer a plurality of toner images onto a sheet, having a endless belt and a plurality of rollers which are spanned by the endless belt, the method having determining an increasing amount of a diameter of a middle section of at least one of a plurality of the rollers in respect to end sections thereof, in accordance with a degree of sub-scanning curvature of an image transferred onto the sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an image forming apparatus where a manufacturing method of a transfer unit, of the present invention is adaptable.

FIG. 2 is a partial view of a transfer unit shown in FIG. 1.

FIG. 3 is a frame format of the transfer unit shown in FIG. 2 as seen from an arrow X1 in FIG. 2.

FIG. 4( a) a diagram showing states of sub-scanning curves by respective colors, using line images as examples of images of respective colors to be transferred onto a sheet P, in case photoconductive substances 1Y, 1M, 1C and 1K, and a intermediate transfer substance 8 are arranged as FIG. 1 shows.

FIG. 4( h) is a diagram where states of sub-scanning curve transferred onto a sheet are indicated by respective colors, where a cyan toner image and a magenta toner image are omitted.

FIG. 5 is a diagram where states of sub-scanning curve transferred and superimposed onto a sheet are indicated.

FIG. 6 is a view where an endless belt is used for a photoconductive substance in a shape of a belt.

FIG. 7 is a view where an endless belt of a transfer unit is used as a sheet conveyance belt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following describes an embodiment of a manufacturing method of a transfer unit related to the present invention with reference to drawings, without the present invention being restricted thereto:

FIG. 1 is a view showing an example of an image forming apparatus to which the manufacturing method of transfer unit related to the present invention can be adapted.

The image forming apparatus related to the present invention is configured with an image forming apparatus main body GH and an image reading apparatus YS. The image forming apparatus main body GH, so called tandem type color image forming apparatus includes a transfer unit 60 having a plurality of sets of image forming sections 10Y, 10M, 10C and 10K, and an intermediated transfer substance 6 in a shape of an endless belt; a sheet feeding section said a fixing device 9.

Above the image forming apparatus main body GH, the image reading apparatus YS configured with an automatic document feeding device 201 and a scanning exposing device 202 is disposed. A document d placed on a document table of the automatic document feeding device 201 is conveyed through conveyance rollers and the image on a single side or both sides of the document d is light scanned through an optical system of scanning exposing device 201 and read by a line image sensor CCD.

Signals formed by photoelectric conversion through the line image sensors CCD are processed by analogue processing, shading correction, A/D conversion and image compression thereafter sent to exposing sections 3Y, 3M, 3C and 3K.

The image forming section 10Y to form a yellow color image is provided with a charging section 2Y, an exposing section 3Y, a developing device 4Y and a cleaning section 8Y at a peripheral of the photoconductive substance in a shape of a drum. The image forming section 10M to form a magenta color image is provided with a charging section 2M, an exposing section 3M, a developing device 4M and a cleaning section 8M at a peripheral of the photoconductive substance in a shape of a drum. The image forming section 10C to form a cyan color image is provided with a charging section 2C, an exposing section 3C, a developing device 4C and a cleaning section 8C at a peripheral of the photoconductive substance in a shape of a drum. The image forming section 10K to form a black color image is provided with a charging section 2K, an exposing section 3K, a developing device 4K and a cleaning section 8K at a peripheral of the photoconductive substance in a shape of a drum.

Meanwhile, each of the developing devices 4Y, 4M, 4C and 4K contains each of yellow (Y), magenta (M), cyan (C) and black (K) binary developing agent including toner and carrier of small particle diameters.

The intermediated transfer* substance 6 trains about a plurality of the rollers, being supported rotatably.

The fixing device 9 includes a first pressure roller 93 having an elastic layer over a core steel; a heating roller 92 having a heater inside; a endless fixing belt training about the first pressure roller 93 and the heating roller 92, a second pressure roller 94 arranged in a position opposite to the first pressure roller 93 in a way that a second pressure roller 94 is in contact with the fixing belt 91 with pressure so as to form a fixing nip section; and fixes toner not yet fixed onto the sheet P with a heat and a pressure when the sheet F passes through the fixing nip section in a direction where the a toner surface of the sheet P before fixing comes in contact with the fixing belt 91.

Thereby, the toner images of respective colors formed through the image forming sections 10Y, 10M, 10C and 10K are subsequently superimposed on the intermediate transfer substance 6 in rotation motion so as to be primary transferred, thus a color toner image where the toner images of respective colors are superimposed is formed. The sheet P stored in a cassette 20 is fed by a sheet feeding section 21 and goes through the sheet feeding rollers 22A, 22B, 22C, 22D and resist roller 23 then is conveyed to a transfer section 7A so as to the color toner image is secondary transferred onto the sheet P. The sheet P on which the color image has been transferred is heated and pressed at a fixing device 9 so that the color image is fixed onto the sheet P. Thereafter, sheet P is grasped by a discharging rollers 24 and loaded on a discharge sheet tray 25 outside the apparatus.

On the other hand, after the color toner image is transferred onto the sheet P through the transfer section 7A, the intermediate transfer substance 6 from which the sheet P is separated by curvature is cleaned by the cleaning section 8A to remove remaining toner.

The following will describe a manufacturing method related to the present invention employing the transfer unit.

FIG. 5 is a frame format of the intermediate transfer substance 6 and rollers 61 and 62 of the transfer unit 60 as seen from an arrow X1 in FIG. 2. The roller 61 is a straight roller and the roller 62 is so-called crown roller where a diameter Dc at middle section is larger than a diameter Ds of the end sections. A crown of the roller 62 is formed in a shape of a straight line or in a shape of a circular arc. In the embodiment of the present invention, a roller 62 is machined in order to realize high accuracy of dimension. However, it is preferable to cast the roller 62 from a view point of the cost, in case a highly accurate steel molding can be used thanks to a large number of the rollers 62 are produced.

An increasing amount of the diameter of the meddle section of the roller 62 in respect to the end sections (Dc-Ds) is determined in accordance with a degree of sub-scanning curvature of the image transferred onto the sheet P.

As FIG. 4 shows, to measure the degree of the sub-scanning curvature, a largest distance of each image in the middle part of the image is measured. The above measurement is carried out by actually measuring the aforesaid largest distance with measuring instruments such as a scale and a magnifier. In the present embodiment, a distance h between the yellow color image and the black color image both having a large sub-scanning curvature is measured.

The measured distance h is assigned as a standard value for the increasing amount of the diameter at the middle section of the roller 62. Using the roller 62 having the standard value, printing test, is further carried out with trimming so as to determine an optimum value.

In the present embodiment, the distance h of the sub-scanning curve is 100 μm, thus 100 μm is assigned to the increasing amount at the roller middle section to inhibit the color shift.

In the above measurement, distance measuring devices such as an image sensor can be used. With the image sensor, a measuring error can be eliminated and an accurate measurement can be easily realized.

Also, in advance, the distortion amount of the rollers 61 and 62 when the intermediate transfer substance 6 is spanned is calculated by means of rigidity calculation. Then a degree of sub-scanning curvature is estimated based on the distortion amount so as to determine a standard value of the increasing amount of the diameter of the middle section of the roller 62. Thus printing test is further carried out with trimming so as to determine the optimum value.

Presumption of the degree of sub-scanning curvature can be carried out by measuring amounts of deformation of the rollers 61 and 62 or the intermediate transfer substance 6 while the rollers are spanned by the intermediate transfer substance 6. Also it can be carried out by measuring a circumferential speed of the intermediate transfer substance 6. As above by presumption of the degree of sub-scanning curvature based on measurement of the actual apparatus, more realistic presumption can be possible.

According to the above embodiment, it is possible to equalize the moving distances of the toner image, which is transferred from the photoconductive substance onto the intermediate substance 6, until the toner image is transferred onto the sheet P at the both ends and at the middle section of the intermediate transfer substance 6, thus the color shift due to sub-scanning curve of the image can be inhibited. Thereby there can be provided a transfer unit 60 capable of forming the high quality image, without having the color shift, using simple parts and the structure with low cost.

In the present embodiment, a photoconductive substances (1Y, 1M, 1C and 1K) have a drum shape, however, they can be in a shape of an endless belt. FIG. 6 shows an example. Since the structure of each color is the same, here yellow color will be described. Rollers 1Y2 and 1Y3 are spanned with a photoconductive substance 1Y1 in the shape of a belt. At a peripheral of the photoconductive substance. 1Y1 training about the roller 1Y3, an unillustrated charging section 2Y, exposing section 3Y, developing section 4Y and cleaning section 8Y are arranged. The configuration conforms to the photoconductive drum shown by FIG. 1. FIG. 6 shows an example where two rollers are spanned by the photoconductive substance 1Y1, and number of the rollers can be more than two. The above structure expands a possibility of arranging the charging section 2Y, the exposing section 3Y, the developing section 4Y and the cleaning section 8Y.

Also, in the present embodiment, the endless belt of the transfer unit 60 was used as the intermediate transfer substance, however in other embodiment, the endless is not used as the intermediate transfer substance, the belt can be used as a sheet conveyance belt. FIG. 7 shows an example of other embodiment of the transfer unit. A transfer section is configured with transfer rollers (7Y, 7M, 7C and 7B) which are arranged opposite to the photoconductive substances via a conveyance belt 6 b. A sheet P is conveyed on the conveyance belt and goes through from a right direction of FIG. 7 so as to transfer an image formed on a photoconductive drum onto the sheet P. In this case, since the sheet P is nipped and conveyed by the photoconductive substances (1Y, 1M, 1C and 1K) and the transfer rollers (7Y, 7M, 7 c and 7 k) via the conveyance belt 6 b, the color shift due to the distortion of rollers 61 b and 62 b occurs in the same manner as above. Therefore, by conforming to the embodiment of the transfer unit shown by FIG. 7, and by increasing the diameter of the middle section of the roller 62 b in respect to the diameters of the end sections in the above method, the color shift due to the sub-scanning curve of image can be inhibited.

According to the above embodiments of the present invention, there can be manufactured a transfer unit, which can inhibit the sub-scanning curve with a simple structure capable of forming the high quality image without having the color shift. 

1. A manufacturing method of a transfer unit to transfer a plurality of toner images transferred from a photo conducive substance onto a sheet, having a endless belt and a plurality of rollers which are spanned by the endless belt, the method comprising: determining an increasing amount of a diameter of a middle section of at least one of a plurality of the rollers in respect to end sections thereof, in accordance with a degree of sub-scanning curvature of an image transferred onto the sheet.
 2. The manufacturing method of claim 1, wherein the rollers are produced by machining.
 3. The manufacturing method of claim 1, wherein the rollers are produced by casting.
 4. The manufacturing method of claim 1, wherein the increasing amount of the diameter of the middle section of the roller is determined based on a measurement value of the degree of sub-scanning curvature of the image transferred onto the sheet.
 5. The manufacturing method of claim 1, wherein the increasing amount of the diameter of the middle section of the roller is determined based on a measurement value of the degree of sub-scanning curvature of the image transferred onto the sheet measured by an image sensor.
 6. The manufacturing method of claim 1, wherein the increasing amount of the diameter of the middle section of the roller is determined by presumption of the degree of sub-scanning curvature in case the image is transferred onto the sheet based on a rigidity calculation of the endless belt and the rollers.
 7. The manufacturing method of claim 1, wherein the increasing amount of the diameter of the middle section of the roller is determined by presumption of the degree of sub-scanning curvature in case the image is transferred onto the sheet based on measurement amounts of distortion of the endless belt and the rollers.
 8. The manufacturing method of claim 1, wherein the increasing amount of the diameter of the middle section of the roller is determined by presumption of the degree of sub-scanning curvature in case the image is transferred onto the sheet based on a measurement circumferential speed of the endless belt.
 9. The manufacturing method of claim 1, wherein the photoconductive substance is in a shape of a drum.
 10. The manufacturing method of claim 1, wherein the photoconductive substance is in a shape of a belt.
 11. The manufacturing method of claim 1, wherein the end less belt is an intermediate transfer substance on which the toner image developed, by developer is transferred.
 12. The manufacturing method of claim 1, wherein the end less belt is a conveyance belt to convey the sheet. 